Catalytic reduction of chloronitro aromatic compounds



United States Patent US. Cl. 260-580 6 Claims ABSTRACT or THE DISCLOSURE A process for producing chloroanilines through the catalytic hydrogenation of a nitro monocarbocyclic aromatic hydrocarbon containing from 1 to 2 chlorine atoms without accompanying dechlorination, such process C0111- prising conducting such catalytic hydrogenation in the presence of a mixture of from 0.01 to 0.08 weight percent of 1 to 5 percent by weight of platinum on carbon and from 0.05 to 0.5 weight percent of a phosphite, e.g. triphenylphosphite or tritolylphosphite. Such catalytic hydrogenation is conducted at a temperature of from 30 to 125 C. and under a hydrogen gas pressure of 100 to 1,500 p.s.i.g.

This invention relates to an improved process of catalytically reducing chloronitro aromatic compounds to the corresponding chlorine substituted amines, and is further concerned with an improved process wherein the said reduction is accomplished substantially without attendant dechlorination.

Aromatic nitro compounds as well as aromatic chloronitro compounds have long been reduced to the corresponding aromatic amines by a great number of different methods, such as, for example, by the use of iron borings and dilute acid. In addition, zinc, tin and stannous chloride, with or without acid, alkaline sulfides and a great variety of other reducing agents have been used. New techniques have been developed within recent years employing molecular hydrogen with various catalysts to effect the direct reduction of nitro compounds to the amines. Such catalytic hydrogenation techniques oifer many advantages over the previously employed chemical methods, especially with respect to economy, versatility, operating complexities, separation of products, and the ease of adaptation to continuous processing. Such catalytic hydrogenation techniques have been used with the aromatic nitro compounds in both liquid and the vapor phase, and a great number of different catalyst systems have been suggested as suitable for the different techniques, primarily because of many inherent disadvantages which come to the front in the use of the catalytic hydrogenation technique.

The major problem encountered in the catalytic reduction of aromatic chloronitro compounds is the extensive dechlorination during the process. Various means have been suggested to suppress this dechlorination, such as, for example, the use of a complex catalyst of copper and chromium, the use of rhodium as a catalyst in the presence of an organic solvent, the use of controlled amounts of magnesium oxide or hydroxide with a platinum on carbon catalyst, and the use of piperazine or morpholine and their N-alkyl substituted derivatives as dechlorination suppressants. The use of a platinum catalyst in conjunction with small amounts of morpholine inhibits dechlorination to the 0.40 to 0.50 mole percent level.

It is the principal object of the present invention to provide an improved process of catalytically reducing chloronitro aromatic compounds wherein the formation of ice dechlorination products is minimized to a level of 0.20 mole percent or even less.

Other objects and advantages will become manifest from the following description.

We have found that the formation of dechlorinated products during the platinum catalyzed reduction of chloronitro aromatic compounds is minimized to a level of 0.20 mole percent or less by conducting the reduction in the presence of triphenylphosphite or tritolylphosphite (mand p-cresyl phos-phites) at a temperature of from 30 to 125 C. and a hydrogen gas pressure of from to about 1,500 p.s.i.g.

In the practice of the present invention, any stainless steel autoclave equipped with a propeller agitator moving at 900 r.p.m., electrical heating, a jacket for cooling, and a gas inlet tube attached to a hydrogen source, and capable of handling pressures up to about 1,500 p.s.i.g. may be employed. Based on the weight of the chloronitro aromatic compound, from 0.01 to 0.08 weight percent of a 1 to 5 percent by weight of platinum on carbon as catalyst and from 0.05 to 0.5 weight percent of either triphenyl phosphite or tritolyl phosphite are added to the autoclave. After purging the autoclave with nitrogen following by hydrogen, the autoclave is heated to between 30 to C. and the unit pressurized to between 100 to 1,500 p.s.i.g. with hydrogen. The lower the temperature, the slower the reduction time. At about 30 C. and a pressure of 100 p.s.i.g, the reduction time may take 17- 19 hours. By increasing the temperature to between 100-125 C. and a pressure to about 300 p.s.i.g. the reduction time is less than one hour. After reduction, the crude chloroamino aromatic compound is discharged from the autoclave, filtered free of catalyst and the water separated. A distillation usually is performed to recover the chloroamine.

The chloronitro aromatic compounds that may be reduced to the corresponding chloroamines in accordance with the present invention include 2-chloronitro benzene; 3-chloronitro benzene; 4-chloronitro benzene; 5- chloro-3-nitro toluene; 4-chloro-2-nitro toluene; 2-chloro- 4-nitro toluene; 6-chloro-4-nitro-l,Z-dimethyl benzene; 4- chloro-Z-nitro-l,3-dimethyl benzene; 6-chloro-4-nitro-l,3- dimethyl benzene; 2,5-dichloronitrobenzene; 3,4-dichloronitrobenzene; and the like including a mixture of crude nitrochlorobenzenes containing about 92% meta isomer, 4-5% of para isomer and 23% ortho isomer. Crudes containing lower content of 3-chloronitrobenzene with 2- chloroand 4-chloronitrobenzenes are just as readily reduced by the process of the present invention without affecting the original isomer ratio. When a chloronitro benzene crude of 99.9% purity, especially of 3-chloronitrobenzene, is employed, the overall yields of 960 of theory of 3-chloroaniline are readily obtained.

The details of the present invention will be apparent from consideration of the following specific examples in which the weight percent of platinum on carbon catalysts and the triphenylor tritolyl phosphite is based on the weight of the chloronitro aromatic compound to be reduced to the corresponding chloroamine.

EXAMPLE 1 Meta-chloronitrobenzene of 99.0 mole percent purity was charged to an autoclave along with 0.05 weight percent of a 5 weight percent platinum on carbon and 0.10 weight percent triphenylphosphite. The autoclave was purged with nitrogen followed by hydrogen and pressurized to 550 p.s.i.g. with hydrogen. The reactants were heated to 60 C. temperature which was maintained until the reaction was completed, 45 hours. The resulting product was cooled and discharged. The reactant was completely reduced to the corresponding chloro aniline and only 0.13 mol percent aniline was detected in the product. A yield, after purification to 99.5% m-chloroaniline, of 93.0% of theory was obtained.

EXAMPLE 2 Example 1 was repeated with the exception that the reactants were heated to 100 C. which was maintained until the reaction was completed, less than 2 hours. Dechlorination was restricted to 0.11% aniline. The yields and quality were the same as in Example 1.

EXAMPLE 3 Example 1 was repeated with the exception that 0.1 weight percent of triphenylphosphite was replaced by 0.05 weight percent and the 0.05 weight percent of weight percent of platinum on carbon was replaced by 0.015 weight percent of 5 weight percent of platinum on carbon as catalyst. The reaction was completed within 6 hours. Dechlorination was restricted to 0.08 mole percent aniline level. The yields and quality were comparable to those obtained in Example 1.

EXAMPLE 4 Example 1 was again repeated with the exception that the autoclave was pressurized from 550 to 1,500 p.s.i.g. and only 0.03 weight percent of 5 weight percent of platinum on carbon was employed as the catalyst along with 0.05 weight percent of triphenylphosphite. Dechlorination was inhibited at the 0.19 mole percent aniline level. The yields and quality were the same as in Example 1.

EXAMPLE 5 2,5-dichloronitrobenzene was charged to an autoclave along with 0.05 weight percent of a 5 weight percent platinum on carbon and 0.05 weight percent of triphenyl phosphite. The autoclave was purged with nitrogen followed by hydrogen and pressurized to 550 p.s.i.g. with hydrogen. The reactants were heated to 75 C. and which temperature was maintained until the reaction was completed, 8 to 9 hours. The resulting product was cooled and ,discharged. The reactant was completely reduced to the corresponding 2,5-dichloroaniline with a trace of m-chloroaniline, less than 0.2 mole percent. A yield, after purification, of 98% of 2,5-dichloroaniline was obtained.

EXAMPLE 6 Example 5 was repeated with the exception that the charge of 2,5-dichloronitr0benzene was replaced by 3,4- dichloronitrobenzene and the temperature increased from 75 to 80 C., at which the reaction mixture was heated and maintained for a period of 9-10 hours. The reactant was completely reduced to the corresponding dichloroaniline with only a trace of chloroaniline, less than 0.25 mole percent. A yield, after purification, was 9798% of 3,4-dichl0roaniline.

EXAMPLE 7 4-chloronitrobenzene was charged to an autoclave along with 0.05 weight percent of a 5 weight percent platinum on carbon and 0.05 weight percent of triphenyl phosphite. The autoclave was purged with nitrogen followed by hydrogen and pressurized to 300 p.s.i.g. with hydrogen. The reactants were heated to 60 C. and the same temperature maintained until the reaction was completed, 8 hours. The resulting product was cooled and discharged. The reactant was completely reduced to the corresponding 4-chloroaniline with only a 0.10 mole percent of aniline as dechlorinated product. A yield, after purification, of 99.5% of 4-chlor0aniline was obtained.

EXAMPLE 8 Example 1 was again repeated with the exception that the m-chloronitrobenzene was replaced by 4-chloro-2-ni. trotoluene. The latter was reduced to 4-chloro-2-aminotoluene with only a trace, less than 0.15 mole percent, of 2-aminotoluene being detected. A yield, after purification, of 99% of p-chlorotoluene was obtained.

It is to be noted that milder temperatures and pressures may be employed to yield satisfactory products. In such case, however, the overall cycle time may be extended to a period of time ranging from less than 2 hours to 24 hours. While platinum on carbon has been employed as the preferred catalyst, other catalysts may be employed with similar satisfactory results, such as, for example, sponge nickel catalyst, platinum black, palladium on charcoal, platinum or palladium on aluminum, and the like.

We claim:

1. A process for minimizing the formation of dechlorinated products during the preparation of chlorine substituted aromatic amines by catalytic hydrogenation of nitro monocarbocyclic aromatic hydrocarbons containing from 1 to 2 chlorine atoms which comprises elfecting the reduction of said nitro aromatic hydrocarbons in the presence of from 0.01 to 0.08 weight percent of 1 to 5 percent by weight of platinum on carbon as catalyst, and in the presence of from 0.05 to 0.5 weight percent of a phosphite selected from the group consisting of triphenylphosphite and tritolylphosphite, based on the weight of said nitro aromatic hydrocarbon, at temperatures of from 30 to 125 C. and hydrogen gas pressure of 100 to 1,500 p.s.i.g.

2. A process according to claim 1 wherein the nitro monocarbocyclic aromatic hydrocarbon is m-chloronitrobenzene.

3. A process according to claim 1 wherein the nitro monocarboxylic aromatic hydrocarbon is 2,5-dichloronitrobenzene.

4. A process according to claim 1 wherein the nitro monocarbocyclic aromatic hydrocarbon is 3,4-dichloronitrobenzene.

5. A process according to claim 1 wherein the nitro monocarbocyclic aromatic hydrocarbon is 4-chloronitrobenzene.

6. A process according to claim 1 wherein the nitro monocarbocyclic aromatic hydrocarbon is 4-chloro-2-nitrotoluene.

References Cited UNITED STATES PATENTS 3,110,747 11/1963 Mullineaux 260580 CHARLES B. PARKER, Primary Examiner P. C. IVES, Assistant Examiner U.S. Cl. X.R. 260689 

